The present invention relates to digital signal magnetic recorders and more particularly to enhanced readback apparatus and methods employable with such recorders.
In digital signal recording, the point of main interest in many cases is the zero crossing of the readback signal. All information is determined based upon such zero signal crossing. Techniques have been used to adjust the zero crossing to convert it to peaks, peak detection, and other forms of signal processing; however, all of these processes have one thing in common--they extract the digital data based upon a predetermined relationship to zero signal crossings.
Digital signal recorders have employed automatic gain control, AGC, in an attempt to enhance detection of the data contained in the readback signal. Further, equalizing and compensation techniques have been used during the recording of such signals, such as the phase compensation taught by Ambrico in U.S. Pat. No. 3,503,059. Also, during readback of such recorded signals, phase adjustments have been made based upon feed forward control, upon wavelength analyses, signal format violations, and most popularly by adjusting the phase of the readback clock using phase lock loop techniques.
All of the above techniques have had varying degrees of success for controlling the detectability of the readback signal. Various techniques are more applicable to one recording density than another recording density. It has been common in the recent past to rapidly increase the recording density of signals on flexible magnetic media. Each time there is a quantum increase in density, there is a corresponding quantum increase in problems associated with detecting the information represented by the readback signal. Accordingly, enhanced signal processing techniques are needed for enhancing the detectability of data contained in high density signals derived from a magnetic recording medium.
A further problem is that a single magnetic medium can be used by a plurality of signal recorders having diverse readback and recording characteristics. Even if the nominal design of a plurality of recorders is the same, variations in manufacturing, head-to-medium spacing, and aging of the various component parts results in a diversity of characteristics among the recorders. This diversity tends to induce errors and limits the capability of recorders to interchange magnetic media while achieving faithful reproduction of recorded information. A second goal is to enhance the interchangeability of the record medium by applying error control techniques to the various signal recorders for enhancing their capability to accommodate permutations induced in the readback signal from any component part changed in any recorder, such changes being unknown or unpredictable.